Phosphorescent display tube having x-y signal grids and control circuitry for same

ABSTRACT

A display device which includes an evacuated envelope, a phosphorescent anode and a plurality of signal grids which control the intensity of electron beams from a cathode. The signal grids are disposed in a double array of parallel wires, each array being positioned at right angles to the other. In the absence of a signal, all the grids are maintained at a negative potential with respect to the cathode. When a small area of the anode is to be illuminated, two grids one from each array, are given positive potentials to send an electron beam from the cathode to the anode and generate light by activating the phosphor. The device also includes an accelerating grid for distributing the electrons evenly over a wide area.

United States Patent 72] Inventor Richard DuBois, Jr. 2,995,682 8/1961Livingston 315/169 Caldwell Township, NJ. 3,042,823 7/1962 Willard 315/169X [21] Appl. No. 766,229 3,144,578 8/1964 Sinclair 3 l3/l09.5X

[22] Filed Oct- 9, 1968 3,406,288 10/1968 Dubois et al 250/217 [45]Patented Feb. 23,197] 2,878,418 3/1959 Garfinkel et al. 3 l 5/68X [73]Assignee Wagner Electric Corporation Primary Examinr lohn w Huckert [54]PHOSPHORESCENT DISPLAY TUBE HAVING X-Y SIGNAL GRIDS AND CONTROL CIRCUITRY FOR Assistant Examiner-Andrew J. James Attorney-Eyre, Mann & Lucaselectron beam from the cathode to the anode and generate light byactivating the phosphor. The device also includes an accelerating gridfor distributing the electrons evenly over a wide area.

PHOSPHORESCENT DISPLAY TUBE HAVING X-Y STGNAL GRIDS AND CONTROLClRCUlTlRY FOR SAME This invention is an improvement over the vacuumdisplay device described in a U.S. lat. application Ser. No. 479,425,filed Aug. l3, 1965, upon which U.S. Pat. No. 3,406,288 issued on Oct.15, i968. The device described in the prior application employed sevenareas of luminescence to produce a stick" design to show digitcharacters on a phosphorescent anode. The present invention employs nomask for limiting the areas of luminescence but instead provides twoarrays of grid wires and means for illuminating any desired spot orcollection of spots over any area of the anode. The anode is perforatedand the phosphorescent material is deposited on the side away from thecathode. The electron beams are directed toward the anode and some or"the electrons pass through the anode perforations, turn around under theinfluence of a reverse electric field and then strike the phosphor. Thereverse electric field is formed between the anode and a transparentconductive coating which may be placed on a transparent nonconductivedisc or directly on the inside surface of the envelope. Pulse controlcircuits are necessary for applying potentials to the signal grid wiresthat the illumination is controlled for any desired area.

One of the features of the invention is an accelerating grid mountedbetween the cathode and the signal grids. This grid is given a positivepotential with respect to the cathode so that it attracts electrons andoperates to distribute the electron intensity evenly over a wide area.

For a better understanding of the present invention, together with otherdetails and features thereof, reference is made to the followingdescription taken in connection with the accompanying drawings.

P16. 1 is a cross-sectional view of one form of the device showing therelative positions of the various components.

HO. 2 is a schematic drawing of the connections showing the two signalgrid arrays, the cathode, and the input connection. Also indicated isone system of operating the device which includes a master clockoscillator, two ring counter circuits, and a divider circuit.

FIG. 3 is a graph indicating the time sequence of some of the pulsesproduced by the circuit shown in FIG. 2.

H6. 4 is a schematic diagram of the display device showing the method ofapplying potentials to the electrodes within the tube.

Referring now to FIG. 1, the device includes a transparent envelope 10,which may be of glass, an electron emissive cathode H, and an anode 12.The anode may be formed of wire mesh or it may be formed of a flat metalplate in which a plurality of holes have been formed by etching orpunching. The anode also includes a phosphorescent coating on the sideof the anode remote from the cathode. An accelerating grid 13 ispositioned adjoining the cathode 11. This grid is formed 'of wireconductors which are spaced so as to form a coarse mesh. The purpose ofthis grid is to distribute the electrons emitted by the cathode. a

Between the accelerating grid 13 and the anode 12 are two arrays ofsignal grids l4 and 15. The first array 14 comprises a plurality ofequally spaced parallel conductors in a first plane. The second array ofgrids 15 is similar to the first but includes a plurality of conductivewires 15 in a second plane parallel to the first and disposed at anangle of 90 to the first array. Each grid wire is connected to aseparate lead-in conductor for the application of controlled operatingpotentials. in order to produce a reverse field for turning theelectrons around after they have passed through the anode, a transparentconductive coating lid is positioned adjoining the anode 12 but on theside away from the cathode. This coating which may be of tin oxide, isalso connected to a lead-in conductor for the application of controlledoperating potentials. This lead-in conductor is generally connected tothe cathode.

The schematic diagram shown in FIG. 2 illustrates the operation of thedevice under one system of controls. in this FlG. there are sixhorizontal grid wires 14 and six vertical grid wires 15. A single clockoscillator 17 provides a series of electric pulses, timed in synchronismwith the input pulses which are applied to terminals 18 and 29. A pairof output conductors 21 sends the pulses from the clock oscillator to afirst ring counter 22, which provides a'series of six sequential outputpulses, each applied to one of the six conductors 23 which are connectedto the six signal grids 15. The clock oscillator 17 also sends its timedpulses to a divider circuit 24 where the frequency of the oscillatoroutput is divided by six and then applied to a second ring counter 25.The second ring counter 25 is also a ring of six, and applies voltagepulses to six conductors 26 in timed sequence so that each of thehorizontal grid wires 14 receives a positivevoltage for the duration ofthe six pulses produced by the first ring counter circuit 22;

The above-described series of pulses and the double array of signalgrids produces a scanning operation which covers the entire area of thegrids 14 and 15. For example, the upper horizontal grid wire 14A isfirst given a positive potential and, while this potential exists, allthe vertical wires are provided with positive pulses which may startwith the left-hand grid 15A and then proceed to the second grid wire 15Band so on until all the vertical grid wires have received positivepulses. Then the secoiid horizontal grid 14B is provided with a positivevoltage by the counter circuit 25 and, while this voltage exists thevertical grid wires 15 received another succession of pulses. Thisaction continues until all the grid wires have received positive pulsesand the entire area has been covered.

The two counter circuits 22 and 25 are employed to raise the potentialsof the grid wires 14 and 15 from a negative value, of about 20 volts, toa more positive value of about 5 volts. The two combinations of 5 voltsat any cross section position is not enough to produce luminescence ofthe phosphor on the anode but when these two voltages are combined withan input pulse applied to terminal 18 the electrons from the cathode 11are sent through the anode, reversed, and then applied to the phosphorto produce a spot of light. it should be noted that an input pulseapplied to terminal 18 and transmitted through diodes 30, is applied toall the horizontal grid wires 14. However, none of the other grids canproduce a stream of electrons since the ones not activated by thecounter circuits are at a potential of about 20 volts negative. In thismanner only a single spot of light will be produced.

It will be obvious to those familiar with ring counters and gatecircuits that the ring countercircuit 25 can be used to operate a seriesof semiconductor AND gates. lf this form of circuitry is applied, diodes30 may be omitted and a single input conductor applied to all the gates.When this form of circuit is operated, the gates are activated insequence and only a single horizontal grid wire will then receive theinput pulse from terminal 18.

The above description has been base on the assumption that the signalsapplied to terminals 18,20 are positive Pulses of maximum amplitude toproduce a light spot having maximum luminance. Such signals will be usedwhenever a symbol, such as a digit, is to be shown. However, if picturesor other indicia are to be shown, the input signals may have variableamplitude, ranging from zero to a maximum value. Intermediate amplitudesignals permit a smaller number of electrons to travel to the anode,thereby producing a gray scale of luminous areas.

it has also been assumed that the signal grids are normally maintainedat a maximum negative value to produce a black or nonluminous anode.While this arrangement conserves the anode power, there may beapplications where the reverse is desired. The signal grids l4 and 15may have a normal potential equal to the cathode potential. Then, whenno signal is present, the anode will show maximum luminance over itsentire area. The picture or indicia are produced by applying negativepotentials to terminals 18, 20 to reduce the potentials of the signalgrids below cathode potential and cut down the luminance oi the anode toproduce a desired light pattern. Several other methods of connecting thedouble array of signal grids are available. While the device has beendescribed as applicable for showing a single character or symbol, it iswithin the range of this invention to expand the dimensions of thedevice with many more grid wires in both dimensions and connect thedevice to a television-receiving circuit for the production oftelevision pictures. in H6. 2 a spot 31 is shown at the intersection ofgrid wires 14B and 15B, this spot being an indication of a spot of lightwhich is produced when the two grid wires are provided with sufficientpositive bias.

Referring now to FIG. 3, the upper row of pulses 33 indicate the outputof the oscillator 17 which may be a free running multivibrator and whichproduces a continuous train of square-topped waves. Pulses 34 representthe voltage pusles produced by the ring counter circuit 22 which appliesvoltage to the vertical grid wires 15 in a sequential manner. Pulse 35represents an input pulse applied to all the horizontal grid wires M butoccuring at the same time as the second vertical grid wire 158 receivesa positive'pulse from counter circuit 22.

Referring now to H6. 4, the power connections to the device areindicated. The transparent conductive layer 16 is connected to thecathode and to the negative terminal of a direct current source. Theanode ll'is connected to the positive terminal of a direct currentsource of supply which may be 250 volts. The space charge grid 13 isconnected to a direct current source of supply which may be 30 volts.The two signal grids M and 15 are connected only to the controlcircuits, shown in block form 38 in this FlGi From the above descriptionof the device and its operation it is evident that a novel display meanshave been shown which can produce an illuminated pattern within a vacuumtube. The pattern consists of a plurality of illuminated areas which aresequentially produced in any desired arrangement by a system of controlcircuitry. p

The foregoing disclosure and drawings are merely illustrative of theprinciples of this invention and are not to be interpreted in a limitingsense. The only limitations are to be determined from the scope of theappended claims.

lclairn:

1. A phosphorescent display tubefor showing a luminous patterncomprising: a transparent evacuated envelope enclosing a cathode foremitting electrons; an accelerating grid positioned adjacent to thecathode for attracting and distributing the electrons emitted by thecathode; a first array of signal grid wires mounted in a planeparallelfto the accelerating grid and including a plurality of spacedparallel conductors, insulated from each other, for controlling the flowof electrons from the cathode; a second array of signal grid wires alsomounted in a plane parallel to the accelerating grid and including aplurality of spaced parallel conductors, insulated from each other, and

disposed at right angles to the wires in the first array; a perforateanode mounted adjacent to the signal grids, said anode having a layer ofphosphorescent material on the side remote from the cathode; a layer oftransparent conducting material disposed between said anode and saidenvelope in a plane in parallel alignment with the anode for creating areverse electric field to reverse the direction of the electrons whichhas passed through the anode perforations and to cause them to strikesaid phosphorescent material on the anode; and a plurality of lead-inconductors sealed in said envelope wall for connection to an externalcircuit, separate lead-in conductors being connected to said cathode, tosaid accelerating grid, to each wire of said first and second arrays ofsignal grid wires, to said anode, and to said layer of transparentconducting material.

2. The display device according to claim 1 wherein said two signal gridarrays define a plurality of square areas, each of said square areasbeing defined by two grid wires from each array, said areas permitting astream of electrons to pass through whenever the bordering wires aregiven a predetermined potential with respect to the cathode.

3. The display device according to claim 1 wherein said layer oftransparent conducting material is deposited on a transqarent insulatoradjacent to the anode.

4. he display device according to claim 1 wherein said layer oftransparent conducting material is deposited on the inside surface ofthe envelope adjacent to the anode.

5. The display device according to claim 1 wherein said layer oftransparent conducting material is electrically connected to thecathode.

6. A display device as claimed in claim 1 wherein said first array ofsignal grid wires is connected to a first pulse generator which appliesa pulse to each of the wires in a sequential manner and then repeats thepulse application at a predetermined rate,

7. A display device as claimed in claim 6 wherein said second array ofsignal grid wires is connected to a second pulse generator which appliesa pulse to each of the wires in a sequential manner and then repeats thepulse application at a predetermined rate.

8. A display device as claim in claim 7 wherein said first and secondpulse generators are coupled to a common oscillator for timing andduration control.

9. A display device as claimed in claim 8 wherein the first and secondgenerators are coupled to the common oscillator by means of ringcounters and divider circuits whereby a single pulse is applied to oneof the wires in the first array during the time each of the wires in thesecond array is pulsed.

1. A phosphorescent display tube for showing a luminous patterncomprising: a transparent evacuated envelope enclosing a cathode foremitting electrons; an accelerating grid positioned adjacent to thecathode for attracting and distributing the electrons emitted by thecathode; a first array of signal grid wires mounted in a plane parallelto the accelerating grid and including a plurality of spaced parallelconductors, insulated from each other, for controlling the flow ofelectrons from the cathode; a second array of signal grid wires alsomounted in a plane parallel to the accelerating grid and including aplurality of spaced parallel conductors, insulated from each other, anddisposed at right angles to the wires in the first array; a perforateanode mounted adjacent to the signal grids, said anode having a layer ofphosphorescent material on the side remote from the cathode; a layer oftransparent conducting material disposed between said anode and saidenvelope in a plane in parallel alignment with the anode for creating areverse electric field to reverse the direction of the electrons whichhas passed through the anode perforations and to cause them to strikesaid phosphorescent material on the anode; and a plurality of lead-inconductors sealed in said envelope wall for connection to an externalcircuit, separate lead-in conductors being connected to said cathode, tosaid accelerating grid, to each wire of said first and second arrays ofsignal grid wires, to said anode, and to said layer of transparentconducting material.
 2. The display device according to claim 1 whereinsaid two signal grid arrays define a plurality of square areas, each ofsaid square areas being defined by two grid wires from each array, saidareas permitting a stream of electrons to pass through whenever thebordering wires are given a predetermined potential with respect to thecathode.
 3. The display device according to claim 1 wherein said layerof transparent conducting material is deposited on a transparentinsulator adjacent to the anode.
 4. The display device according toclaim 1 wherein said layer of transparent conducting material isdeposited on the inside surface of the envelope adjacent to the anode.5. The display device according to claim 1 wherein said layer oftransparent conducting material is electrically connected to thecathode.
 6. A display device as claimed in claim 1 wherein said firstarray of signal grid wires is connected to a first pulse generator whichapplies a pulse to each of the wires in a sequential manner and thenrepeats the pulse application at a predetermined rate.
 7. A displaydevice as claimed in claim 6 wherein said second array of signal gridwires is connected to a second pulse generator which applies a pulse toeach of the wires in a sequential manner and then repeats the pulseapplication at a predetermined rate.
 8. A display device as claim inclaim 7 wherein said first and second pulse generators are coupled to acommon oscillator for timing and duration control.
 9. A display deviceas claimed in claim 8 wherein the first and second generators arecoupled to the common oscillator by means of ring counters and dividercircuits whereby a single pulse is applied to one of the wires in thefirst array during the time each of the wires in the second array ispulsed.